1. Field of the Invention
This invention relates to blood withdrawal devices of the type which employ a sealed vacuum tube, and particularly, a device of this type equipped with a guard member that protects against accidental needle sticks.
2. Background Discussion
In U.S. patent application Ser. No. 07/035,434, entitled, "Medical Device", filed Ap. 7, 1987, assigned to the same assignee of this application, there is disclosed a blood withdrawal device equipped with a needle guard. This device is used with a sealed vacuum tube that is inserted in a tube holding section having a needle recessed within this section. Upon insertion of the sealed end of the tube into the tube holding section, the needle tip punctures the seal and allows blood to flow through the needle into the tube. The other end of the needle has already been inserted into the body of the patient and the vacuum in the tube sucks the blood from the patient so that the blood flows through the hollow shaft of the needle into the tube.
The portion of the needle extending outwardly from the tube holder section is equipped with a guard. The needle has a locking element attached to the needle shaft extending from the tube holding section and the guard is mounted on the shaft. The guard is movable axially between a retracted position where the tip of the needle is exposed so that it may be inserted into the body of the patient and a forward position where the guard covers the tip of the needle. Upon withdrawing the needle from the body of the patient, the guard is moved forward to cover the tip and prevent accidental needle sticks. The locking element along the needle shaft permanently locks the guard in the forward position.
In U.S. patent application Ser. No. 07/037,325, entitled,"Medical Device", filed Apr. 13, 1987, and assigned to the same assignee as this patent application, there is disclosed an improvement in the locking element. There is a problem in mounting the locking element to the shaft of the needle and the Medical Device disclosed in the '325 patent application overcomes this problem. The solution provided is to employ a locking member that has an elongated stem made of a polymeric material and this stem is bonded to the needle shaft during molding. As the stem is being formed about the needle shaft, pressure is applied to the molten plastic material which, upon cooling, shrinks and bonds the surface of the shaft of the needle to the stem.